Removal of Residual Additive Enabling Perfect Crystallization of Photovoltaic Perovskites

Achieving high‐efficiency perovskite solar cells (PSCs) hinges on the precise control of the perovskite film crystallization process, often improved by the inclusion of additives. While dimethyl sulfoxide (DMSO) is traditionally used to manage this process, its removal from the films is problematic. In this work, methyl phenyl sulfoxide (MPSO) was employed instead of DMSO to slow the crystallization rate, as MPSO is more easily removed from the perovskite structure. The electron delocalization associated with the benzene ring in MPSO decreases the electron density around the oxygen atom in the sulfoxide group, thus reducing its interaction with PbI2. This strategy not only sustains the formation of a crystallization‐slowing intermediate phase but also simplifies the elimination of the additive. Consequently, the optimized PSCs achieved a leading power conversion efficiency (PCE) of 25.95% along with exceptional stability. This strategy provides a novel method for fine‐tuning perovskite crystallization to enhance the overall performance of photovoltaic devices.